1. Field of the Invention
This invention relates to a new and useful invention concerning fluid curtain scrubbing of gas borne waste material, a scrubber device, and a method for capture of the gas borne waste materials. The waste material may be a liquid waste entrained in a gas, such as paint entrained in air after spraying the paint onto an article in a spray booth, a particulate waste entrained in a gas, such as dust contained in flue gas, and/or a gaseous waste, such as NOx or SOx contained in flue gas, by way of example but not limitation. The fluid curtain may be a gas such as air or a liquid such as water or a solvent.
More particularly, the invention relates to a venturi scrubber plate and a waste capture system and method employing the venturi scrubber plate. In one embodiment useful as a waste paint capture system for a paint spraying booth, water flows down a flood sheet positioned downstream of paint spray heads and entrains paint overspray to minimize buildup of paint on the interior of the booth. The water from the flood sheet flows into a trough which additionally receives water from a primary scrubber section. An exhaust fan draws air from the spray booth through the trough and through a throat section leading to the primary scrubber section where a flow of water knocks down remaining waste materials from the air flow before it is exhausted through the exhaust fan. Waste paint capture is improved by positioning a perforated plate over the trough so that the waste paint laden air from the spray booth is sucked through the perforated plate with an advantageous venturi scrubbing effect.
The novel venturi scrubber plate is configured to effectively control air velocity through the plate, preferably in a range of from about 1000 to about 2000 linear feet per minute. This advantageously results in a high turbulence profile for the flow akin to misting or atomization which improves paint capture by up to a factor of three times. Contact with paint detacification chemicals contained in the water is advantageously improved so that paint particle formation is inhibited and dectacification efficiency increased.
2. Description of the Prior Art
Scrubbers are know and work on the general principle of employing a fluid curtain to entrain gases, droplets and/or particles. Passing a stream of airborne material through a water curtain, for example, serves to at least entrain and possibly dissolve (a) gases, such as NOx and SOx contained in flue gases, (b) droplets, such as waste paint from a spray operation or any entrained liquid in droplet form, and/or (c) particles, such as fly ash contained in flue gas or powder from an electrostatic coating operation such as paint, sugar, salt, or other such commodities.
The scrubber curtain is typically a water curtain, but may be almost any fluid including liquids, such as solvents, for example, alcohols having 1-8 carbon atoms, and gases, such as a curtain of air or inert gas,flowing at a rate chosen to be effective to knock down material to be removed.
Fluid curtains are known in the art as described in, for example, U.S. Pat. Nos. 4,700,615 and 4,946,718 to Stanley Napadow, the disclosures of which are herein incorporated by reference.
U.S. Pat. No. 4,946,718 describes an air curtain protection system for article conveyors of product treatment booths including a paint spraying booth, washer or filter air cleaning system, and baking oven. Product support members extend through a slot provided in a conveyor mechanism housing into the product treatment booth. A blower forces ambient air through a supply nozzle formed by a plenum on one side of the slot and draws air through a suction nozzle formed by a second plenum on the opposite side of the slot to form a high velocity stream or curtain of air across the slot. This reduces the ingress of deleterious heat or atmosphere from the product treatment booth into the conveyor mechanism housing so that a measure of protect is afforded the conveyor and heat is conserved.
A spray booth including both air and water curtains is described in U.S. Pat. No. 4,700,615. Air flows from a plenum provided under a roof assembly of the booth down to the floor and through side plenums and a throat to wash the interior side walls as an air curtain to prevent adherence of paint particles on the side walls. Water curtains are provided within an air cleaning apparatus positioned under the booth floor through which the down flowing air from the spray booth is pulled by a blower. The flowing air is directed through a series of water curtains to an outlet slot where the air velocity is increased and then slowed down in a larger volume separation chamber where water and air are separated. The direction of air and water flow are reversed several times as the air flows serially through the water curtains the concept being to obtain turbulent air/water mixing so that the particles are wetted and brought down by their increased weight. The water and air are discharged into a large precipitation chamber in which the water is collected and the air velocity is reduced substantially before discharge through an air exhaust duct.
An additional waste paint capturing system 10 currently used in an industrial, high volume spray booth is schematically illustrated in cross-section in FIG. 1 (Prior Art). Articles 1 are transported by a conveyor means 5 through spray booth 10. Spray heads 15 direct paint 20 onto the articles 1. An exhaust means 25 removes air 30 and paint overspray 35 from the booth as an air flow 40 to a primary scrubber section 45 which includes a clean water supply means 46 and a water curtain 48. Within the booth 10, water 50 flows from a clean water supply means 55 down a flood sheet 60 positioned downstream of paint spray heads 15 and entrains paint overspray 35 to minimize buildup of paint on the interior of booth 10. The water 50 from the flood sheet 60 flows as a water curtain 65 into a trough 70 which additionally receives water 48 from the primary scrubber section 45. The exhaust means 25 draws the air flow 40 from the spray booth 10 across the trough 70, through the water curtain 65 and through a throat section 75 leading to the primary scrubber section 45 where the flow of water 48 wets and knocks down remaining waste paint 35 from the air flow 40 before it is exhausted through exhaust means 25. The industry standard air velocity across the throat section 75 of the primary scrubber section 45 for effective water wash scrubbing of paint overspray ranges from 1500 to 1750 linear feet per minute. A flow of scrubbed air 80 exits the paint capturing system 10 through the exhaust means 25.
The effectiveness of such conventional waste capture systems including scrubbers to entrain and remove waste gases, droplets and/or particles leaves much to be desired, however. The costs of downtime and filters required for general maintenance and cleaning of waste capture systems remains excessive, particularly waste paint capture systems where accumulations on booth surfaces is a substantial problem.
Accordingly, it is an object of the present invention to provide a waste material capture system and method having a higher efficiency of waste material capture whether solid, e.g., flue dust or particulates from a powder or electrostatic spray operation such a commodities, for example, sugar and salt, liquid, e.g., paint or other sprayable compositions, or gaseous, e.g., noxious gasses such as NOx and/or SOx, than that previously known in the prior art.
It is another object of the present invention to provide a waste material capture system and method which permits significantly reduced downtime for cleaning of surfaces, changing of filters, and general maintenance, and thereby significantly reduces operational costs.
It is yet another object of the present invention to provide a waste paint capture system which permits significantly reduced downtime for cleaning of spray booth surfaces, changing of filters, and general maintenance, and thereby significantly reduces operational costs attendant to paint spray booth operation, especially an industrial, large scale, paint spray booth operation.
These and other objects are accomplished by the present invention by providing a venturi scrubber plate for a waste capture system for a waste material entrained in a fluid flow, which waste capture system includes an enclosure having a flood sheet over which a liquid flows into a collection trough, an exhaust means which draws the fluid flow containing the waste material from the enclosure, across the collection trough, and through a throat section to a primary scrubber section, the venturi scrubber plate comprising: a plate which is mounted on and substantially covers the collection trough, which has defined therein a plurality of holes, and through which the fluid flow containing the waste material flows, wherein the plate imposes a venturi effect on the fluid flow effective to accelerate the fluid flow so that turbulent mixing of the fluid flow containing the waste material and the liquid takes place and results in improved capture of waste material by the liquid ahead of the primary scrubber section.
The venturi scrubber plate may additionally comprising a plurality of collection tubes extending downwardly from respective ones of the plurality of holes toward the liquid flowing in the collection trough. The plurality of collection tubes may have respective heights which are graduated to maintain an approximately constant spacing between the liquid flowing in the collection trough and the collection tubes. The plurality of holes in the plate may be spaced apart in a regularly array or in a staggered array. The plurality of holes have a diameter and are present in a number effective to accelerate the fluid flow and provide a flow velocity ranging from about 1000 to about 2000 linear feet per minute across the throat section of the primary scrubber section, preferably from about 1500 to about 2000 linear feet per minute, most preferably from about 1500 to about 1750 linear feet per minute.
The waste material may be at least one material selected from the group consisting of a gas, a liquid, and a solid. The gas may be at least one noxious gas such as flue gas, NOx and/or SOx. The liquid may be paint or any other sprayable composition. The solid may be one of flue dust or commodities to be powder coated such as sugar and salt.
The fluid may be a gas such as air or an inert gas. The liquid may be a solvent such as water and/or an alcohol having from 1 to 8 carbon atoms.
These and other objects are accomplished by the present invention by providing a waste capture system for a waste material entrained in a fluid flow, comprising a venturi scrubber plate as described above.
These and other objects are accomplished by the present invention by providing, in a spraying apparatus comprised of an enclosure having a flood sheet over which a liquid flows into a collection trough, an exhaust means which draws a fluid flow containing waste material from the enclosure, across the collection trough, and through a throat section to a primary scrubber section, the improvement comprising: a venturi scrubber plate as described above mounted on and substantially covering the collection trough.
These and other objects are accomplished by the present invention by providing a method for capture of waste material entrained in a fluid flow, comprising the steps of: providing an enclosure having a flood sheet over which a liquid flows into a collection trough; providing an exhaust means which draws the fluid flow containing the waste material through the enclosure, across the collection trough, and through a throat section to a primary scrubber section; and mounting a venturi scrubber plate according to claim 1 to substantially cover the collection trough, wherein the venturi scrubber plate imposes a venturi effect on the fluid flow effective to accelerate the fluid flow so that turbulent mixing of the fluid flow containing the waste material and the liquid takes place and results in improved capture of waste material by the liquid ahead of the primary scrubber section.
These and other objects are accomplished by the present invention by providing a venturi scrubber plate for a waste paint capture system for a waste paint entrained in an air flow, which waste paint capture system includes an spray booth enclosure having a flood sheet over which water flows into a collection trough, an exhaust means which draws the air flow containing the waste paint from the spray booth enclosure, across the collection trough, and through a throat section to a primary scrubber section, the venturi scrubber plate comprising: a plate which is mounted on and substantially covers the collection trough, which has defined therein a plurality of holes, and through which the air flow containing the waste paint flows, wherein the plate imposes a venturi effect on the air flow effective to accelerate the air flow so that turbulent mixing of the air flow containing the waste paint and the water takes place and results in improved capture of waste paint by the water ahead of the primary scrubber section.
The venturi scrubber plate may additionally comprise a plurality of collection tubes extending downwardly from respective ones of the plurality of holes toward the water flowing in the collection trough. The plurality of collection tubes may have respective heights which are graduated to maintain an approximately constant spacing between the water flowing in the collection trough and the collection tubes. The plurality of holes in the plate may be spaced apart in a regular array or in a staggered array. The plurality of holes may have a diameter and be present in a number effective to accelerate the air flow and provide a flow velocity ranging from about 1000 to about 2000 linear feet per minute, preferably from about 1500 to about 2000 linear feet per minute, more preferably from about 1500 to about 1750 linear feet per minute, across the throat section of the primary scrubber section.
These and other objects are accomplished by the present invention by providing a waste paint capture system for waste paint entrained in an air flow, comprising a venturi scrubber plate as described above.
These and other objects arc accomplished by the present invention by, in a spraying apparatus comprised of an spray booth enclosure having a flood sheet over which water flows into a collection trough, an exhaust means which draws an air flow containing waste paint from the enclosure, across the collection trough, and through a throat section to a primary scrubber section, the improvement comprising: a venturi scrubber plate as described above mounted on and substantially covering the collection trough.
These and other objects are accomplished by the present invention by providing a method for capture of waste paint entrained in an air flow, comprising the steps of providing an enclosure having a flood sheet over which water flows into a collection trough; providing an exhaust means which draws the air flow containing the waste material through the enclosure, across the collection trough, and through a throat section to a primary scrubber section; and mounting a venturi scrubber plate as described above to substantially cover the collection trough, wherein the venturi scrubber plate imposes a venturi effect on the air flow effective to accelerate the air flow so that turbulent mixing of the air flow containing the waste paint and the water takes place and results in improved capture of waste paint by the water ahead of the primary scrubber section.
The method may further comprise including at least one additive in the water selected from the group consisting of a surfactant, an anti-foaming agent, and a detacifier. The method may further comprise including an additive in the water which is a detacifier effective to bind with reactive end groups of polymeric constituents of the paint, such as a formaldehyde amine.